Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $198.47   7.808%   $213.9665   $213.97   $213.95   $214.00  
  Purchase #2 $161.93   3.541%   $167.6639   $167.66   $167.65   $167.70  
  Purchase #3 $60.34   13.266%   $68.3447   $68.34   $68.35   $68.30  
  Purchase #4 $243.57   10.303%   $268.665   $268.67   $268.65   $268.70  
  Purchase #5 $210.86   3.475%   $218.1874   $218.19   $218.20   $218.20  
  Purchase #6 $98.49   13.371%   $111.6591   $111.66   $111.65   $111.70  
  Purchase #7 $237.56   9.775%   $260.7815   $260.78   $260.80   $260.80  
  7 purchase totals = $1,211.22       $1,309.2681   $1,309.27   $1,309.25   $1,309.40